Warming World Could Thin the Fat in Tropical Dairy Milk by 2100

Milk is one of the most climate-sensitive foods on the planet, and a new study from Brazil suggests that the damage done by a warming atmosphere will not stop at the farm gate. It will trickle all the way into the price farmers are paid. Researchers analyzed three years of records from 25 commercial dairy farms in the humid tropical state of São Paulo, representing 1,025 lactating Holstein cows, and linked environmental data to raw-milk composition, microbiological quality, and quality-based payments. Their exploratory projections under a moderate warming scenario to the year 2100 point to a slow but steady erosion of milk fat and a rise in bacterial counts, with only part of that deterioration reflected in the economic signals farmers receive.

The study, published in the Journal of Agriculture and Food Research, is unusual because it treats climate, milk quality, and money as a single connected system. Most previous work has examined heat stress effects on milk yield or composition in isolation, leaving a gap between the biology of the cow and the economics of the bulk tank. By integrating all three dimensions, the Brazilian team set out to ask a deceptively simple question: when the climate changes the milk, does the paycheck change with it?

To answer it, the researchers assembled an unusually complete dataset. Hourly records of air temperature and relative humidity from the Agronomic Institute meteorological station in Piracicaba, totaling 25,920 observations, were aggregated into monthly means to match the resolution of milk-quality data from the Milk Quality Reference Laboratory. Fat and protein percentages were measured by near-infrared reflectance spectroscopy, somatic cell counts by Fourier-transform infrared spectroscopy, and standard plate counts of bacteria by flow cytometry. Gross milk prices came from the Center for Advanced Studies in Applied Economics at ESALQ-USP, and quality bonuses and penalties were calculated using the published pricing criteria of the processor Piracanjuba, aligned with Brazilian Normative Instructions 76 and 77. After harmonization, the final analytical dataset consisted of 36 consecutive monthly observations from January 2016 to December 2018, with no missing values.

The seasonal patterns were striking. Air temperature averaged 25 degrees Celsius in summer and 23.6 in spring, well above the roughly 24-degree upper critical temperature generally cited for lactating dairy cows, while fall and winter averages of about 20 degrees remained within the thermoneutral range. Relative humidity hovered between 64 and 73 percent, high enough in the hot seasons to limit evaporative heat dissipation, the primary cooling mechanism available to cattle. Milk fat told the mirror-image story: it peaked at 3.62 percent in fall and fell to 3.23 percent in spring, while protein followed the same trajectory. The final milk price averaged R$ 1.48 per liter in the cool seasons against R$ 1.23 in the hot ones, a gap driven largely by composition-linked bonuses. Notably, somatic cell count and standard plate count showed no significant seasonal differences, which the authors attribute to the strict, standardized milking hygiene protocols all participating farms followed, including pre- and post-dipping and standardized cup handling.

The multivariate analyses reinforced the picture. Principal component analysis showed the final milk price negatively associated with air temperature and bacterial count, and positively associated with fat and protein. Canonical discriminant analysis separated the four seasons with 88.9 percent classification accuracy, with air temperature, milk fat, and final price contributing most strongly to the discrimination. Canonical correlation analysis then quantified the link between the thermal environment and the milk-quality-economic variable set, revealing approximately 36 percent shared variance between the two canonical variates. The authors are careful to stress that this figure represents shared variation between linear combinations of variables, not the proportion of total milk-quality variation caused by climate; genetics, nutrition, lactation stage, hygiene, and management all contribute substantially. Within the environmental set, air temperature dominated the canonical relationship and was negatively associated with milk fat and its economic component, while relative humidity played a comparatively weak role in this particular dataset.

To look forward, the team fitted both ordinary least squares regression and a deliberately constrained Gradient Boosting Regressor, using an expanding-window temporal validation in which each of the 12 months of 2018 was predicted using only preceding data. The nonlinear model consistently outperformed the linear one, but the authors emphasize that performance metrics from a 36-month series are exploratory evidence, not externally validated forecasts. When the fitted relationships were combined with the IPCC RCP4.5 warming scenario, the clearest directional signal was a decline in milk fat: a statistically significant negative coefficient, with the conditional trajectory falling from roughly 3.31 percent in 2025 to 3.21 percent by 2100. The fat-linked bonus approached zero over the same horizon, and the final milk price was projected to slip from about R$ 1.21 to R$ 1.12 per liter, an absolute decrease of roughly R$ 0.09, or about 7.4 percent.

Milk protein, by contrast, showed only a weak and statistically non-significant negative trend, drifting from about 3.14 to 3.11 percent, and the protein bonus barely moved. The microbiological story was different in kind. Standard plate count rose along the warming trajectory, from approximately 0.99 million to more than 1.13 million colony-forming units per milliliter by 2100, though the low explanatory power of the model indicates that climate accounts for only a small share of the variation in bacterial load. Somatic cell count showed no significant relationship with warming. The most provocative finding, however, was economic: within the evaluated payment structure, the SPC- and SCC-linked payment components remained essentially flat and statistically unrelated to the warming trajectory, even as the underlying bacterial counts climbed.

That asymmetry between biological deterioration and economic signal may be the study’s most consequential message. If quality-based payment schemes respond strongly to compositional traits like fat but weakly to gradual increases in microbiological counts, then the market may fail to warn producers about a climate-driven hygiene risk until it crosses a penalty threshold. The authors suggest that more responsive pricing could incorporate progressive penalties or bonuses tied to microbiological indicators and climate-related risks, but they caution that simply raising penalties could disproportionately burden smallholders with limited capital for cooling, sanitation, and infrastructure. Any redesign of incentives, they argue, should be paired with technical assistance and access to adaptation technologies. They also note that the findings are specific to one Brazilian payment structure and cannot be generalized to processors or markets with different thresholds and weights.

The authors are equally candid about the limits of their projections. Extrapolating relationships estimated from three years of data to the end of the century assumes that those relationships remain stable, ignoring future genetic selection for heat tolerance, changes in nutrition, housing, cooling technology, and market policy. Environmental exposure was characterized by a single external weather station rather than on-farm sensors, and no physiological or behavioral measures of heat stress were collected, so the results describe system-level associations rather than cow-level mechanisms. The trajectories should be read for their direction and relative magnitude, not as precise predictions for any given year. Even so, the study offers a rare integrated view of how a warming, humid tropics will press simultaneously on milk composition, hygiene, and farm income, and it makes a compelling case that climate adaptation in dairy farming must be designed around the whole chain, from shade and silage to somatic cells and the fine print of the milk check.

Subject of Research: Climate change effects on milk quality and farmer remuneration in humid tropical dairy systems

Article Title: Climate–milk quality–remuneration relationships in humid tropical dairy systems: an exploratory assessment under climate-change scenarios to 2100

Article References: Silveira, R. M. F., de Castro Júnior, S. L., Roma Junior, L. C., McManus, C., & da Silva, I. J. O. (2026). Climate–milk quality–remuneration relationships in humid tropical dairy systems: an exploratory assessment under climate-change scenarios to 2100. Journal of Agriculture and Food Research, Article 103369. https://doi.org/10.1016/j.jafr.2026.103369

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103369

Keywords: climate change, dairy farming, milk quality, heat stress, Holstein cows, milk fat, somatic cell count, standard plate count, quality-based payment, RCP4.5, Brazil, tropical agriculture